1. Field of the Invention
This invention relates to enclosures or booths for use in spray coating, and more particularly to an improved enclosure for use in individually spray-coating large articles being conveyed in closely spaced relation on a conveyor.
2. Description of the Prior Art
It is known in the art to coat large articles at a coating station while the articles are supported on a conveyor for movement past the station. For example, in the steel industry, metal strip formed on a rolling mill is wound into large coils which are conveyed from the rolling operation by a chain and pedestal-type conveyor. Such coils are frequently coated with oil to prevent or control corrosion during storage or shipping and this coating is accomplished while the coils are supported on the conveyor pedestals. In the past, it has been the practice to momentarily stop the conveyor and manually coat the coils using a hand manipulated hose and nozzle for "spraying" or flowing the coating oil over the surface of the coil.
The prior art manual coil spraying operation has not been satisfactory for several reasons. For example, in the brief time alloted for coating each coil, it is not always possible to apply the oil uniformly, making it necessary to use an excess of oil which not only adds to the cost of the operation but also results in substantial oil drainage from a coated coil after it is moved from the coating station. Also, use of a hand manipulated nozzle to coat the coils inherently results in oil being sprayed or deflected onto adjacent equipment as well as onto the floor at and around the coating station, thereby producing a serious safety hazard. Further, because of the end use or the nature of the individual coils, it is frequently necessary or desirable to avoid application of oil to specific coils moving on the conveyor, and the open air manual coil coating operation frequently results in oil contamination of such coils, particularly when large coils are positioned in closely spaced relation on the conveyor.
It is known to provide a coating hood along a conveyor line for containing and removing airborne coating particles and vapors produced by spraying operations within the hood. For example, U.S. Pat. No. 3,842,793 discloses a system for coating glass bottles within a hood as the bottles are moved through the hood on a conveyor. The hood disclosed in this patent is supported for vertical movement out of the path of the conveyed bottles in the event of a log jam. Such hoods conventionally are open ended, forming a tunnel through which the articles to be coated pass in an atmosphere containing the coating material or a spray of the coating material, with the hood being continuously evacuated to prevent escape of the coating material into the environment.
Coating booths are also known in which doors are provided to completely enclose articles being coated. For example, U.S. Pat. Nos. 4,133,255 and 4,231,289 disclose booths for use in spray coating automobiles, with each booth having a door at its end which may be opened to permit a vehicle to be driven into the booth, then closed for the spraying operation. Means for continuously circulating atmosphere through the booth for removing paint vapors and particles is provided. A flexible, roll-up door or curtain is employed by the paint spray booth of the '289 patent.
The manual oil coating of steel coils normally involves application of the oil by a low pressure spraying or flooding process from nozzles designed to cover a relatively large area rather than an atomizing or misting spray of the type conventionally employed in paint booths or the like. While such an operation may result in droplets of oil being projected or deflected from the target coil to thereby contaminate the surrounding area, the relatively heavy oils used generally settle quickly and do not present an environmental hazard in the atmosphere. Thus, it has not been considered necessary to provide an evacuated enclosure and sophisticated precipitation or filtering devices for removing droplets and vapors of such oils from the atmosphere. Nevertheless, droplets of oil do tend to accumulate on surrounding structure and floor areas and it is therefore desirable to contain the oil spray. Use of conventional enclosures, however, present problems in that the oil accumulation tends to run or drop from the overhead structure to contaminate coils passing therethrough which are not to receive the oil coating. Further, the size of a booth required for enclosing the large coils and the close proximity of the coils to one another on the conveyor makes it impractical to use conventional doors on the booth. For example, swinging doors present a problem in that there is insufficient distance between the coils to permit their operation. Laterally sliding doors can project into corridor space adjacent the conveyor to present an obstruction or hazard to traffic or personnel in this area, while oil from vertically sliding doors can drain onto coils which are not to be oiled as they pass through the booth on the conveyor.
It is therefore an object of the present invention to provide an improved coating system for use in oil coating metal coils which are moved seriatim through the booth on a conveyor.
It is another object to provide such a system including a booth having a movable top wall which may be closed during a spraying operation and opened to permit a coil to be moved into and through the booth without contamination from oil dropping from the top wall.
Another object is to provide such a booth having fixed sidewalls and movable end closures or doors which may be opened and closed without interference from the closely spaced coils on the conveyor.
Another object is to provide such a coating booth which is inexpensive to construct, which requires a minimum of space, and which effectively contains oil from a plurality of spray nozzles located in the booth during spray coating a coil in the booth.